Fixed minor memory leak in framebuffer attachments.

Fixed minor memory leak in framebuffer attachments.

Renderbuffers and texture attachments to framebuffer objects overwrite
each other, and so should the links that preserve their JavaScript
wrappers.

This is difficult to test because there's no guarantee of prompt
reclamation. Ensured expando-loss.html test still runs.

BUG=547946
Committed: https://crrev.com/e473a2d937f3ded6565367a9c00f89fc4e6e90ff
Cr-Commit-Position: refs/heads/master@{#356189}

[Ken Russell (switch to Gerrit), 2015-10-26 21:20:05]

kbr@chromium.org changed reviewers:
+ bajones@chromium.org, zmo@chromium.org

[Ken Russell (switch to Gerrit), 2015-10-26 21:20:06]

PTAL. Please CQ if this looks OK to you. Thanks.

[Zhenyao Mo, 2015-10-26 22:03:48]

LGTM

[Zhenyao Mo, 2015-10-26 22:03:53]

The CQ bit was checked by zmo@chromium.org

[commit-bot: I haz the power, 2015-10-26 22:05:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1415873007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1415873007/1

[commit-bot: I haz the power, 2015-10-27 00:05:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-27 00:06:58]

Patchset 1 (id:??) landed as
https://crrev.com/e473a2d937f3ded6565367a9c00f89fc4e6e90ff
Cr-Commit-Position: refs/heads/master@{#356189}